The present invention relates to a three-dimensional shape measuring device for measuring a three-dimensional shape of an object by an optical non-contact method.
In a known method for measuring a shape of a three-dimensional object, a surface of the object is traced by a tracer disk and a contour of the tracer disk is plotted by a pen to determine the shape of the object by an envelope of the plotted pattern. This method has disadvantages in that it is a contact method, measuring accuracy is poor because the shape is determined by the envelope and a long measuring time is required. In one prior art optical non-contact method, a laser beam is irradiated on an object and imaged on a position detector from a direction different from the direction of irradiation to determine a three-dimensional shape by a signal level from the position detector. In another prior art method, a relative distance between an entire measuring system and an object is varied so that an image is focused at a center of a position detector. Such optical methods, however, are highly affected by a reflection characteristic of the object so that accurate measurement from a position signal of a reflected light is not attained. More particularly, a light intensity received by the position detector varies in two orders depending on the reflection characteristic of the surface of the object and relative relations between a normal direction of the surface and the direction of laser beam irradiation, and the direction of imaging. Because of such variation in the light intensity, it has been difficult to accurately determine the position.